KEY WEST, Fla  The Florida Keys, already dealing with invasive exotics from melaleuca to iguanas, have added another to the list of unwanted newcomers: the African Gambian pouch rat.

Biologists and conservationists in the Keys say the rodent needs to be eradicated, before it increases its range and harms native species that live in natural areas of the Keys.

Although it is unclear how or why the rat -- which can grow as big as a raccoon -- was released on Grassy Key, biologists are saying the animal could be devastating to the Florida Keys' ecological system.

The omnivores, or animals that eat almost everything, could compete for food with endangered species such as the silver rice rat, carry diseases and eat bird eggs.

And the greater threat is that the pouch rat could make it to Key Largo, threatening the endangered wood rat, biologists say. And, even worse, the rat that can grow up to nine pounds might make it to the Florida Everglades.

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"There's no telling what would happen if they made it to the mainland," biologist Randy Grau said.

Grau, who works as a wildlife biologist for the Florida Fish and Wildlife Conservation Commission, says the rat needs to be exterminated. Grau said it could be difficult for the rats to make it across the long bridges to Key Largo and Big Pine Key.

"But they could get in the back of a truck and make it that way," he said.

Grau said the Grassy Key pouch rats are the first documented breeding population in the United States.

"It's another Florida Keys first," he said.

There have been unconfirmed reports that Gambian pouch rats have made it to Key Largo, but thorough surveys have not revealed any evidence.

So far, there are no takers to eradicate the rat. Government agencies have not stepped up to fund a project to eliminate the pests.

Chris Bergh, chairman of the Florida Keys Invasive Exotic Task Force, said the exotic rats could harm rare and protected plants. The rats, which get their names because they have pouches in their cheeks, could eat fruits on plants, he said.

"If the rats eat the fruit, it could prevent plants from spreading as they should," Bergh said.

Another problem is that the rats are so big, they may not have any natural predators.

Neil Perry, who is writing a thesis for his Texas A&M master's degree while studying in the Keys, said the rats are probably too big for birds of prey to eat.

Perry is studying the population of the silver rice rat and the Lower Keys marsh rabbit in the Keys.

Cats, which are predators of the endangered species Perry is studying, don't mess with the Gambian pouch rat, he said.

Connie Faast, who lives on Grassy Key, had the giant rats living under her house. One night, she said, she heard loud screeches in the street. The rats were fighting.

"Two cats were on the side of the road just watching the rats," Faast said.

The male pouch rats are aggressive when they encounter one another.

But, Chris Sutton, who lives on Grassy Key, said the rats are otherwise extremely friendly.

"They get along with everything," she said. "They're tame animals to start with, and they are not afraid of people."

Sutton says the rats eat out of the same dish as her cats and dogs, and her friend saw one of the rats eating out of a bird feeder.

However, Sutton said, she has not see as many of the big rats anymore.

Faast also said she has not seen as many rats recently, but she knows they are still there.

"Ever since we started trapping under my house, they haven't been back," Faast said. She thinks the rats are too smart to go to a place where they were previously trapped.

Rumor has it that eight rats were let out five years ago, Perry said, one male and seven females. The rats have up to four litters every nine months, with up to six offspring in litters.

There is no telling how many of the rats are living on Grassy Key now, he said.

Grau said he hopes to show people the threat of the rat is imminent. He hopes the attention will spark the state or a U.S. wildlife agency into action.

"Hopefully, it will get attention, and decisions can be made here to deal with them," Grau said.